1. Field of the Invention
The present invention relates generally to photovoltaic cells and, more particularly, to an improved photovoltaic cell that combines the technology of electrostatic bonding with total internal reflection to provide a cell assembly with improved conversion efficiency.
2. The Prior Art
Solar cells generally are formed with a front surface partially covered by thin front contact grid lines, also referred to as front surface metallization. The front surface metallization of a solar cell must satisfy several conflicting requirements, such as: (1) the metal coverage of the front surface of the solar cell must be low in order to minimize losses due to the shadowing of the cell surface; (2) the distance from any point on the cell front surface to the nearest metallization element must be short in order to minimize sheet resistance losses in the front surface layer; (3) resistance along the metal grid lines and the conductor bus must be low; and (4) contact resistance between the metallization element and the semiconductor front surface must be low in order to minimize power losses due to these resistances.
One attempt at solving the problem of illumination blocked by the grid lines of the front surface metallization for use with flat plate solar cells involved the provision of a plurality of converging lenses which concentrate the illumination onto the active cell areas rather than being reflected from the front surface metallization. See U.S. Pat. No. 4,053,327, issued to Meulenberg, Jr. on Oct. 11, 1977. These plurality of converging lenses are formed in a plastic or glass cover slide for terrestrial use or formed in glass, fused silica, quartz or sapphire for space applications, and is shown attached to the top surface of the solar cell by a layer of adhesive.
Another attempt at solving the problem of blocked illumination by the grid lines of the front surface metallization for use with optical concentrators, such as involving the use of Fresnel lenses, included the application of a flexible cell cover formed of an optically clear, flexible material, such as a silicone polymer. A plurality of prisms are formed in the outer surface of the cell cover such that the incident illumination is refracted by the prisms onto the active cell areas rather than onto the metallic conducting elements. See the U.S. Pat. No. 4,711,972, granted to O'Neill on Dec. 8, 1987.
The former Meulenberg design, when exposed to environmental conditions, has performed below expectations. It was also expensive to manufacture. Additionally, the cover tended to become misaligned due to mismatch in the thermal expansion coefficients between the cover material and the cell material, degrading its performance. The latter O'Neill design, on the other hand, using the flexible silicone polymer tends to degrade over time due to exposure to ultraviolet and charged particle radiation, as well as due to mechanical erosion.
There is thus room for improvement in the construction of photovoltaic cells.